Whether the Holocaust happened is no longer up for debate at Southern California's Rialto Unified School District.

The initial assignment given to eighth-graders in the San Bernardino County district was to do some research and write an essay explaining whether they believed the Holocaust was a real historical event or a political scheme to influence public emotion and gain.

"It was an error," district spokeswoman Syeda Jafri said Monday.

Several groups, including the Anti-Defamation League, called or emailed the school objecting to the assignment.

One person made a number of calls to police with some very specific death threats, said Rialto police Capt. Randy De Anda.

The threats were specific and directed at Jafri and interim Superintendent Mohammad Z. Islam, De Anda said.

There was no protest or any other action on campus Monday, but because the department takes death threats very seriously, De Anda said he and two officers were on campus checking them out.

"We believe he (the caller) is a white male in his 30s. He did give us a name, but we haven't confirmed it yet so we don't know if he's a previous student," De Anda said.

The department has all the calls on tape and will complete its investigation and forward it to the district attorney.

A team of teachers will meet to revise the assignment, Jafri said, and Islam will talk to the district's education services department to ensure all references to the Holocaust "not occurring" are stricken on any current or future argumentative research assignment.

"The Holocaust should be taught in classrooms with sensitivity and profound consideration to the victims who endured the atrocities committed," Jafri said. "We believe in the words of George Santayana, those who cannot learn from history are bound to repeat it."